The infrastructure of a typical data center is being challenged by the burgeoning growth of cloud computing and mobile internet data usage. Data centers all over the world are transforming the network architectures and fiber network systems to keep place with current needs and future-proof networks to meet higher network capacity. Besides the shift of the network architecture, a major significant transformation is the upgrade of data speeds across the network. For switch-to-switch connections, 10 Gb/s connection links are replaced by 40 Gb/s and 100 Gb/s systems, based on wavelength division multiplexing (WDM) technologies which utilize four wavelength light for transmission signals in parallel. Furthermore, the number of servers and floor space also increase to an unprecedented scale. The footprint, cost and power consumption of optical modules become a significant factor. Thus, integrated multiplexing/de-multiplexing (Mux/DeMux) components are required for module packaging to combine lights of four wavelengths into one output beam at the transmitter port or to separate four-wavelength signals out of a mixed beam at a receiver port.
A conventional coupling lens for Mux/DeMux is illustrated in Error! Reference source not found.3, formed by adhering two lenses and one right-angle prism together. The glass lens 1 and glass lens 2 are fabricated by high-temperature molding, and the right-angle prism is fabricated by polishing lens. As such, the fabrication procedures of these components are cost ineffective. Error! Reference source not found. shows the coupling function of an optical coupling device. The output port of the waveguide is fixed at the focus point of glass lens 1, which turns the incoming light into parallel light. A parallel light is then reflected toward glass lens 2, and is focused by glass lens 2 at the focus point, where a photodiode is placed. The optical system requires that all the optical components to be placed exactly in the designed optical path; otherwise the coupling efficiency from waveguide to the photodiode is low. The fabrication procedure of a conventional coupling lens based on glue-bonding confines the alignment precision, or otherwise the fabrication cost is high.